A producing well extracts oil and/or natural gas from one or more subsurface reservoirs of hydrocarbons. The development of a producing well includes drilling a borehole into the subsurface ground, casing the drilled borehole or leaving the borehole uncased, and completing the borehole to enable production.
After drilling a well for hydrocarbons, it may be necessary to perforate the walls of the well to facilitate flow of hydrocarbons into the well. Wells require perforation because the drilling process causes damage to the formation immediately adjacent to the well. This damage reduces or eliminates the pores through which the oil or gas would otherwise flow. Perforating the well creates a channel through the damage to undamaged portions of the formation. The hydrocarbons flow through the formation pores into the perforation channels and through the perforation channels into the well itself.
Traditional methods of perforating the well (both casing and the formation) involved lowering tools that contain explosive materials into the well adjacent to the hydrocarbon bearing formation. Discharge of the explosive would either propel a projectile through the casing and into the formation or, in the case of shaped charges, directly create a channel with explosive force. Such devices and methods are well known in the art.
In vertical wells, gravity may be used to lower the perforating device into position with wireline being used to hold the device against gravity and retrieve the device after discharge. For lateral wells, which may be horizontal or nearly horizontal, gravity may only be used to lower the perforating device with wireline to a point where the friction of the device against the well bore overcomes the gravitational force. The perforating device must then be either pushed or pulled along the lateral portion of the well until the device reaches the desired location.
Along with perforating the formation, packers may be used to isolate a section of the well for selective production and/or other downhole operations. A packer is a common downhole tool used in both the drilling and completion of a well. A packer typically has a sealing element, a holding or setting device, and a fluid passageway. Packers may be, but are not limited to, pneumatically or hydraulically expandable, swellable through use of a fluid, or expanded through fluid diffusion. Additionally, packers may seal through an elastomeric element that is solid and expands outwards under axial compression or tension. Production packers are used in completions to isolate an annulus between the casing or liner and the production tubing; and also between the open hole and a wellbore section. By creating a seal in the annulus, production control is achieved and tasks such as testing, fluid injection, perforation, treatment, and zonal isolation can be accomplished.
Expandable packers may be used for different sealing and partitioning purposes in boreholes. Typically, an annular packer is connected to a pipe, such as a production or injection pipe, which is run into the borehole, after which, the annular packer is expanded against the formation wall or against a casing. Smaller packers may also be used within smaller tubulars within a wellbore to achieve desired sealing and partitioning.